Ultraviolet (UV) radiation is a form of electromagnetic energy with wavelengths shorter than visible light and longer than X rays. It spans from roughly 100 to 400 nanometres and is subdivided into UVA, UVB and UVC bands based on biological effects and atmospheric absorption.
Spectrum and biological effects
UVA (315–400 nm) accounts for most of the UV light reaching Earth’s surface and penetrates deep into the skin, generating reactive oxygen species that contribute to photoaging. UVB (280–315 nm) has higher energy, causing direct DNA damage by inducing cyclobutane pyrimidine dimers, leading to mutagenesis and skin cancers; it also initiates vitamin D synthesis in the skin. UVC (100–280 nm) is the most energetic and germicidal portion of the spectrum; it is absorbed by the ozone layer and does not normally reach the ground. In microbes, UVC and UVB radiation disrupt replication by forming thymine dimers and other photoproducts in nucleic acids. Cells counteract this damage through photolyase‑mediated photoreactivation or nucleotide excision repair pathways. Overexposure to UV radiation in humans leads to erythema, cataracts and immunosuppression, while controlled exposure has therapeutic applications such as treating psoriasis.
Applications in microbiology and health
The germicidal properties of UVC are exploited in biosafety cabinets, operating theatres and water purification systems to reduce microbial contamination. Low‑pressure mercury lamps emitting at 254 nm are commonly used to disinfect air and surfaces in laboratories; newer excimer lamps at 222 nm may provide similar efficacy with reduced harm to human skin. UV radiation is also used to crosslink nucleic acids in molecular biology and to inactivate viruses for vaccine production. In public health, UV index forecasts inform sun protection strategies. While UV exposure contributes to skin cancer incidence, it is essential for vitamin D synthesis and has roles in circadian rhythm regulation.
Ultraviolet radiation encompasses a range of wavelengths with diverse biological effects. Understanding its spectrum enables safe application in disinfection, medicine and environmental health.
Related Terms: Electromagnetic Spectrum, Ionizing Radiation, DNA Damage, Sterilization, Photoreactivation